local mfl, mce = math.floor, math.ceil
local n = io.read("*n")
if n < 100 then
  local a = 0
  for i = 10, n do
    if i % 3 == 0 then a = a + 1 end
  end
  print(a) os.exit()
end
local t = {}
while 0 < n do
  table.insert(t, n % 10)
  n = mfl(n / 10)
end
local max, normal = 1, 0
do
  local v = t[#t]
  if v % 3 == 0 then
    max = 1
    normal = mfl(v / 3)
  else
    max = 0
    normal = mfl(v / 3) + 1
  end
end
for i = #t - 1, 1, -1 do
  if max == 1 then
    local v = t[i]
    if v % 3 == 0 then
      normal = normal * 4 + mfl(v / 3)
    else
      normal = normal * 4 + mfl(v / 3) + 1
      max = 0
    end
  else
    normal = normal * 4
  end
end
local ret = normal + max - 4 --0,3,6,9

z = {}
for i = 10, 99 do
  if i % 3 == 0 then
    if (i % 10) % 3 ~= 0 then
      ret = ret + 1
    end
  end
end
print(ret)